The present invention relates to a novel agricultural chemical system and method and, more particularly, to a system that senses the chemical condition of the soil in real time and applies an appropriate amount of corrective agricultural chemical or fertilizer in response to a sensed deficit or excess condition. This system has important benefits in cost reduction, energy resource conservation, crop production, and reduction of environmental degradation.
The modern farm practice of applying chemicals to the soil to obtain optimal crop yield differs little from that used a hundred years ago, when manure from farm animals and so-called "green manure" (composed of luguminous crops or harvest detritus) were added. The farmer, as always, desires sufficient soil fertility to ensure that a successful harvest will result from his planting. The methods by which the farmer's objectives are met have advanced considerably. Cropland productivity is increased many-fold with the application of specific chemical materials tailored to precisely provide the plant nourishment or protection needed. Beyond the need for adequate fertility, the crop is usually also given protection from competing weeds and insects by the application of assorted herbicides and insecticides.
Fertilizers and agricultural chemicals are applied by diverse types of field equipment, including granular spreaders, liquid spray bars, and anhydrous, solution, or granular injectors. Farmers also make choices as to when to apply the fertilizer for the next growing season, such as in the late fall or early spring, while planting, or after planting. Similarly, agricultural chemicals such as herbicides are applied at an appropriate stage of weed growth most likely to destroy or regulate undesireable plant growth.
Assorted variables influence the amount of nitrogen and other nutrients that are available for plant growth and development. In the case of nitrogen, local field conditions determine the quantity of ammonium held on the exchange complex of the soil and the precise mechanics of conversion to more available forms via bacterial action. Conversion of variable ammonium levels at distributed oxidation levels in soils is highly variable from point-to-point even within fields which appear relatively homogeneous. Although this extreme variability of soil chemical levels has been known since at least the 1920's, until now no one has perfected a method of accounting for this variability while adding fertilizers or other corrective chemicals such as lime.
Nitrogen exists in the soil in a variety of chemical forms. In the ammonium form it is relatively immobile, but after transformation by soil bacteria to nitrate its mobility increases drastically. Nitrate becomes elusive because of its high solubility in soil water. Nitrate moves with the soil water in response to soil temperature changes, rainfall, and crop transpiration demands. The coefficient of variation of soil nitrate levels typically has a mean of 50% and often reaches 100% even over small areas of only several square yards. Similar observations have been made for pH and potassium levels. Because available nitrogen varies widely, even when fields have been uniformly fertilized, sporadic, conventional soil samples cannot be representatve indicators of a field's nitrogen availability status.
Insufficient nutrient levels will affect crop productivity adversely; excess nutrient levels will either have a similar effect or simply be wasted. In the case of nitrogen, soil nitrate (NO.sub.3 --N) levels above 30 ppm are considered to be wasted nutrients. Field data indicate that considerable excess nitrate is available that does not contribute to crop production. Because nitrate is mobile and does move downward away from the rooting zone in the absence of a crop, nitrate in the soil at the end of a growing season may not be available to the next year's crop but may serve only to contaminate ground water.
Plants use only those nutrients they need and the use of the nutrients complies with a law of diminishing returns. Above a certain threshold level, the farmer obtains little yield response with increasing nutrient level. From an energy efficiency perspective, nutrients applied above this threshold level are wasted. In the case of a normal distribution with a large coefficient of variation (ratio of standard deviation to the mean value), approximately 50% of the nutrients are wasted. This means that both the energy and raw materials used to manufacture the nutrient, as well as the farmer's profit dollars, have been squandered.
For example, nitrogen in its gaseous form is of no use to plants. Plants require that nitrogen, in the form of complex nitrogen compounds, be further transformed into soluble nitrates in order to be utilized by the plants. All agricultural chemical compounds, including manure, are toxic to some extent and can contaminate groundwater, particularly those in the nitrate form. Thus amounts of fertilizer greatly in excess of what the plants can profitably use cannot be prudently applied. They are also expensive, which is another good reason to not overfertilize cropland. Until the present invention, the farmer has had no practical way to optimize his application rate, nor to vary his application rate in response to changing conditions across his field. He has been limited to simply applying what worked in the past, perhaps aided by his recollection of how last year's crop came out, perhaps supplemented by a few spot soil analyses made around the field.
Because of the spatial variations in his field, and because of the time delay between sampling and receiving results--during which the soil conditions will have changed--the farmer who has paid for spot samples is scarcely better able to fertilize his fields than is the farmer who simply fertilizes on an historic basis. Consequently, farmers routinely apply excess fertilizer as a protective measure, and in doing so lower their profit margin and risk groundwater contamination, neither of which is desirable.
Farmers know, qualitatively, that crop yields vary because uniformly applied fertilizers are not converted uniformly to forms useful to plants. Farmers generally use rules of thumb to guide application timing. Moreover, farmers realize that their only source of agrichemical recommendations beyond accepted rules of thumb is either an extension agent or a chemical sales representative.
Soil sampling, used to aid the farmer in fertilizer application, is conventionally based on a farmer's own sample timing and site selection rationale. Chemical analyses of soil samples that the farmer provides to the extension system agent or salesman require interpretation by technically trained personnel to reveal nutrient needs. Often, however, either no nutrient analysis is performed or the analysis is ignored as meaningless due to the perceived complexity of the technical issues in agricultural chemical management. Today, generalized nitrogen management recommendations are all based on experimental evaluation of different fertilizer treatment methods. Soil tests are not routinely done for available nitrogen at the farm level, and the "turnaround" time between sampling and receiving laboratory results is too long to satisfy the farmer's needs for the timing of his application. Local, spatial variations which have significant effects on the crop are normally not addressed at all.
Accordingly, significant energy waste occurs in the application of agricultural chemicals simply because no proven, economical method exists to properly and timely allocate chemicals to meet crop needs, and agricultural chemicals and fertilizers are consequently applied in substantially uniform amounts irrespective of local variations in soil chemical conditions.
In summary, the conventional method of providing agrichemical recommendations for farm level chemical application includes soil sampling by the farmer himself and laboratory analyses, resulting in technically informed interpretations by technically trained personnel. These recommendations normally are then implemented by the farmer himself, who usually is not technically trained in these disciplines.
There are significant sources of error in this multiple-step process, including, for example, errors unavoidably caused by the time delay and errors in selecting a truly representative sample, sample collection and handling, sample preparation and conditioning in the laboratory, trained interpretation of nutrient needs, and errors in application of the recommended level due to the imprecision of the chemical application equipment.